The present invention belongs to the domain “safety in the technical drive and control system for, for instance, machine tools”. A motor serves in a machine tool inter alia to change a tool's position and speed or, as the case may be, rotational speed. For example magnetic or optical transmitter systems are located directly on the motor in order to register said position and speed. Optical transmitter systems, for example, include a light-emitting diode that sends light to two phototransistors via a glass disk that is provided with slits and rotates with the motor. The phototransistors' signals are the transmitter system's output signals and are in particular sinusoidal and cosinusoidal. Said signals must be evaluated in such a way as to obtain at least one actual position value for the tool. It should further be possible to determine the tool's revolution rate or speed from the position and sampling time. The setpoint position value is predetermined by the geometry of the work piece being worked. The position controller uses the actual position value for setting the setpoint position value.
The sine and cosine curves are interpolated by electronic circuitry to produce the actual position value. An analog-to-digital converter converts the analog signals into digital signals and the number of zero crossings of the sine or, as the case may be, cosine curves is determined in order to establish the ordinal of the sine or, as the case may be, cosine curve currently being fed out by the transmitter system. To finely determine the angle, the sine is divided by the cosine and the tangential arc determined from the resulting value. Because the glass disk provided with slits has, for example, 2,048 slits, 2,048 sine or, as the case may be, cosine curves are obtained for each revolution of the motor. The tangential arc can have been resolved repeatedly into, for example, 2,048 individual steps. Approximately four million possible items of information will thus be obtained for each revolution of the motor.
The cited electronic circuitry is, though, very interference-prone. To allow for its proneness to interference, two channels are employed in the prior art:
The signals from the transmitter are processed mutually independently in two identical channels. The actual position value determined by one channel is compared with the actual position value determined in the other. If the actual position values tally within certain tolerances, then the actual position value of one of the two channels will be used as the output signal. There will be an error message if the two channels' actual position values do not tally. Because the position controller will no longer be able to operate reliably, the entire machine will be stopped.
It is a requirement of Germany's TÜV (Technical Supervision Authority) or, as the case may be, of that country's em-ployer's liability insurance association for the two channels, which are provided by means of electronic components on sili-con chips, not to be provided on the same chip or at least to be separated by means of a silicon trench. The reason is that similar errors not detectable through the mutual comparison of the channels may otherwise occur in channels 1 and 2.
The consequences of providing two different chips are high costs and large space requirements. A plurality of housings have to be provided. Although a possibility, the solution em-ploying a silicon trench is uneconomical because the trench width will need to accord with the specific ambient tempera-ture range. An increase in temperature due to a defect in one channel must not lead to an impermissible increase in tempera-ture in the other. For applications having high permissible ambient temperatures the silicon surface will accordingly in-crease uneconomically as its portion of the trench.
Described in U.S. Pat. No. 4,079,374 is a system for analyzing sinusoidal and cosinusoidal input signals onto which a phase has been impressed by a resolver. A first phase-locked loop feeds the phase out. A second phase-locked loop can be provided which feeds out a derivation of the phase.